COMP2221COMP2221

Networks Networks

in in OrganisationsOrganisations

Richard HensonRichard Henson

February 2012February 2012

Week 1: Standards and Week 1: Standards and Computer NetworksComputer Networks

ObjectivesObjectives– Explain evolution of data transmission Explain evolution of data transmission

through networksthrough networks– Define standardsDefine standards– Explain how standards work and why they Explain how standards work and why they

are so important for digital networksare so important for digital networks

History of Electricity-basedHistory of Electricity-basedCommunication NetworksCommunication Networks

Used for centuries before Used for centuries before organisations used Computers…organisations used Computers…

Chronologically:Chronologically:– Telegraph (1840s) Telegraph (1840s) – Telephone (1910s)Telephone (1910s)– Telex (1930s)Telex (1930s)– Internet/first digital WANs (1970s)Internet/first digital WANs (1970s)

Each network developed its Each network developed its own standards for…own standards for…

Creation of dataCreation of data Format of transmitted dataFormat of transmitted data VoltageVoltage Error-checkingError-checking Receiving, storing, presentation Receiving, storing, presentation

of transmitted dataof transmitted data

National and International National and International NetworksNetworks

Telegraph :transmitted data within a particular Telegraph :transmitted data within a particular countrycountry– developed National standardsdeveloped National standards

» e.g. in the UK… BS standarde.g. in the UK… BS standard

Telephone:Telephone:– initially National standardsinitially National standards– developed International callingdeveloped International calling

» French-based standards became the Internationally French-based standards became the Internationally recognised ones (CCITT)recognised ones (CCITT)

» CComité omité CConsultatif onsultatif IInternational nternational TTéléphonique et éléphonique et TTélégraphiqueélégraphique

A tale of standards…A tale of standards…

Roman Empire, AD 0Roman Empire, AD 0– urban streets were open sewersurban streets were open sewers

Created Passing places createdCreated Passing places created– stone paths across the streetstone paths across the street

Needed to leave spaces for Needed to leave spaces for chariot wheelschariot wheels– how wide?how wide?

What width to choose?What width to choose?

SStandard “wheelbase” width agreed (4’ 8½’’)tandard “wheelbase” width agreed (4’ 8½’’) Used for chariots throughout Roman EmpireUsed for chariots throughout Roman Empire Revived in UK as Revived in UK as ““standard gaugestandard gauge” for ” for

railway tracks (1830s)railway tracks (1830s)– most railways around the world still use the 4’ 8most railways around the world still use the 4’ 8½½

standard to this daystandard to this day– even Space Shuttle was transported on 4’ 8even Space Shuttle was transported on 4’ 8½’’ ½’’

tracks (!)tracks (!)

Breaking a standard?Breaking a standard? Why stick to standard gauge?Why stick to standard gauge?

– everyone else uses it!everyone else uses it! MMost powerful railway company in the UK ost powerful railway company in the UK

(GWR: The Great Western Railway) tried to (GWR: The Great Western Railway) tried to changechange the standard width of a track the standard width of a track to 6’ 0’’ to 6’ 0’’– used the 6’ “Broad Gauge” for all their tracksused the 6’ “Broad Gauge” for all their tracks– wider carriages, more passenger comfort…wider carriages, more passenger comfort…

Other railways maintainOther railways maintaineded 4’ 8½’’ !!! 4’ 8½’’ !!! GWR GWR eventually gave up and converted all eventually gave up and converted all

their tracks to the standard gaugetheir tracks to the standard gauge

  Lessons from this storyLessons from this story

Large, powerful organisations try to Large, powerful organisations try to make their own standards universalmake their own standards universal

Existing standards are difficult to Existing standards are difficult to changechange

Once established, standards may well Once established, standards may well be adopted world-widebe adopted world-wide

Standards therefore need to be right!Standards therefore need to be right!

CCITT and Computer CCITT and Computer StandardsStandards

In the early days, CCITT laid down the In the early days, CCITT laid down the standard… (like the Romans…)standard… (like the Romans…)

More recently, CCITT became ITU:More recently, CCITT became ITU:– International Telecommunication UnionInternational Telecommunication Union

Through ITU, many CCITT standards applied Through ITU, many CCITT standards applied to computer networks:to computer networks:– Group 3: protocol for sending fax documents Group 3: protocol for sending fax documents

across (analogue) telephone linesacross (analogue) telephone lines– Group 4: protocol for sending fax documents over Group 4: protocol for sending fax documents over

ISDN networks (more on these later)ISDN networks (more on these later)– ““V” modem standardsV” modem standards

Comparison of Computer Comparison of Computer & Telecoms Networks& Telecoms Networks

Information sent is digital (!)Information sent is digital (!)– all prior CCITT etc. standards were all prior CCITT etc. standards were

analogue…analogue…– potential range of uses of devices are potential range of uses of devices are

much more flexiblemuch more flexible

Control doesn’t have to be centralisedControl doesn’t have to be centralised– fundamental difference with CCITT-fundamental difference with CCITT-

standardised networksstandardised networks

Standards in ComputingStandards in Computing

Area of rapid changeArea of rapid change EEarly emerging standard…arly emerging standard…

– may be eclipsed by nemay be eclipsed by new w technologytechnology SStandards tandards usuallyusually follow many years after the follow many years after the

products themselves have been on the products themselves have been on the marketmarket

Means tMeans they are often based on specific hey are often based on specific productsproducts ( (usually the market leader at the usually the market leader at the timetime!)!)

StandardsStandards

Definition:

– “A standard is an established or accepted model”

Communication protocols…

– “Elements of a communication system that are

defined by an agreed set of rules, conditions,

parameters or methods”

Type of StandardsType of Standards

De FactoDe Facto– A product or service that is a standard by A product or service that is a standard by

virtue of its widespread use by interested virtue of its widespread use by interested usersusers

De JureDe Jure– The standard devised by a committee of the The standard devised by a committee of the

organisation or, a working group of a organisation or, a working group of a subcommittee of a committee of the subcommittee of a committee of the organisationorganisation

Standards and IT ProfessionalsStandards and IT Professionals

Standards:Standards:– ensure that products can communicateensure that products can communicate– identify incompatibilities between productsidentify incompatibilities between products– provide a check that customers are buying provide a check that customers are buying

the correct productthe correct product– ensure that customers are not buying a ensure that customers are not buying a

manufacturer dependent productmanufacturer dependent product

ISO (International Standards Organisation)

Been providing International standards for many areas

Even for management systems:– ISO9001– ISO14001– ISO27001

ISO Development Process (1)

ISO standards panel convened: experts ISO standards panel convened: experts in the relevant fieldin the relevant field1.1.decide the contents of the definition of draft decide the contents of the definition of draft

standard standard 2.2.proposal passed to the parent committee proposal passed to the parent committee

for ratification before publication as, first, a for ratification before publication as, first, a draft for discussion (DD)draft for discussion (DD)

ISO Development Process (2)

Once ratified, it becomes a draft Once ratified, it becomes a draft international standard international standard

Once the document has been available Once the document has been available for a certain amount of time…for a certain amount of time…– allowing full scrutiny… allowing full scrutiny… – it becomes a full International Standard (an it becomes a full International Standard (an

ISO)ISO)

ProprietaryProprietary Systems Systems

BBig computer manufacturers in the ig computer manufacturers in the 1960s and 1970s 1960s and 1970s worked independently worked independently to produce their own softwareto produce their own software

TTeams of researchers to develop their eams of researchers to develop their own systems for communicating own systems for communicating between devicesbetween devices

DifferentDifferent research teams research teams, , differentdifferent company aimscompany aims, so , so products products incompatibleincompatible

ProprietaryProprietary Systems Systems  

CConsidered to be a good thing by companies onsidered to be a good thing by companies such as IBM and ICL, because it “locked” such as IBM and ICL, because it “locked” customers into their productscustomers into their products

NNot popular with customers, who wanted to ot popular with customers, who wanted to be able to buy more freelybe able to buy more freely

AAlso a barrier to communicationlso a barrier to communication::– between companiesbetween companies– sometimes between sometimes between different parts of the same different parts of the same

companycompany BecauseBecause they were using incompatible they were using incompatible

systemssystems

Open SystemsOpen Systems

ISO aware thatISO aware that the basic infrastructure the basic infrastructure for for global digital communicationsglobal digital communications was rapidly was rapidly emerging in the form of the Interneemerging in the form of the Internett

ISOISO decided that thdecided that the existing proprietary e existing proprietary isolationist stance was isolationist stance was not condunot condussive to the ive to the growth of effective digital data growth of effective digital data communications on a world-wide basiscommunications on a world-wide basis

ISO aISO agreed that what was needed was greed that what was needed was open open systemssystems

Open SystemsOpen Systems

Definition: Definition: – ““a computer system that is ‘open’ for the purpose a computer system that is ‘open’ for the purpose

of information exchange”of information exchange” Open systems are therefore not restrOpen systems are therefore not restricted to icted to

one particular manufacturers own system of one particular manufacturers own system of communicatingcommunicating

Open systems should provideOpen systems should provide t the ability tohe ability to::– interchange applications and datainterchange applications and data– between systems with different underlying between systems with different underlying

hardware and softwarehardware and software

Open Systems Interconnect (?)Open Systems Interconnect (?) HHistoric meetings in Geneva co-ordinated by istoric meetings in Geneva co-ordinated by

ISO (back in ISO (back in 1977, 1978)1977, 1978) Involved proprietary systems manufacturers, Involved proprietary systems manufacturers,

telecomms companies and researcherstelecomms companies and researchers AgreedAgreed to produce to produce a software modela software model for for

open systemsopen systems– accepted that this would take years to achieveaccepted that this would take years to achieve– the industry couldthe industry could, however,, however, at least aspire to at least aspire to this this

in new developments…in new developments… MModel became known as the odel became known as the Open Systems Open Systems

Interconnection model (OSI model)Interconnection model (OSI model)

LANs, WANs, StandardsLANs, WANs, Standards The PC changed everything…The PC changed everything… When it became possible to network When it became possible to network

PCs, new sets of protocols and PCs, new sets of protocols and technologies were developed & usedtechnologies were developed & used– new classification required:new classification required:

» LAN: generally applied to PC/Unix networks LAN: generally applied to PC/Unix networks within institutions (IEEE)within institutions (IEEE)

» WAN: existing networks that covered longer WAN: existing networks that covered longer distances (CCITT??? ISO???)distances (CCITT??? ISO???)

OSI Model & WAN standardsOSI Model & WAN standards

OSI soon caught onOSI soon caught on– challenge to CCITTchallenge to CCITT– teamed up with IEEE (802 standards) teamed up with IEEE (802 standards)

In 1984, OSI became an International In 1984, OSI became an International Standard (!)Standard (!)– open systems had credibility!!!open systems had credibility!!!– Proprietary systems had competition…Proprietary systems had competition…

Why link PCs together to Why link PCs together to make LANs (revision)make LANs (revision)

Workshop in small groupsWorkshop in small groups Each group - four reasonsEach group - four reasons Ten minutesTen minutes

What makes up a LAN (1)?What makes up a LAN (1)?

Hardware:Hardware:– computers and other network devicescomputers and other network devices

» e.g. printers, web camerase.g. printers, web cameras

– transmission media, transmission media, e.g. cable, radio e.g. cable, radio waveswaves

– network cardsnetwork cards, which link the network , which link the network devices to the transmission mediadevices to the transmission media

What makes up a LAN (2)?What makes up a LAN (2)? SoftwareSoftware to (just a sample…) to (just a sample…)

– send/receive datasend/receive data– provide an even flow of data between devicesprovide an even flow of data between devices– make sure sent data goes to the right placemake sure sent data goes to the right place– provide a path for data through the networkprovide a path for data through the network– make sure data is checked for corruption as it make sure data is checked for corruption as it

passes through the networkpasses through the network– anything else that may need to be done to the anything else that may need to be done to the

data e.g. formatting, compression, encryptiondata e.g. formatting, compression, encryption

Some reasons to keep PCs Some reasons to keep PCs “standalone”“standalone”

Workshops again…Workshops again… Another four reasonsAnother four reasons Ten minutesTen minutes

Transfer of data Transfer of data through LANsthrough LANs

Cables designed to transmit high Cables designed to transmit high volumes of digital data volumes of digital data

Network cards provide the computer-Network cards provide the computer-medium interface:medium interface:– control flow rate and error checking of datacontrol flow rate and error checking of data– send/receive data at high, and even send/receive data at high, and even

higher… speedshigher… speeds

LAN connectionsLAN connections

Computers physically connected using:Computers physically connected using:– cabling (or e/m radiation of an appropriate cabling (or e/m radiation of an appropriate

frequency)frequency)– network cardsnetwork cards– networking softwarenetworking software

If a cabled LAN connection exceeds:If a cabled LAN connection exceeds:– 100 metres (twisted pair cabling)100 metres (twisted pair cabling)– 185 metres (coaxial cabling) 185 metres (coaxial cabling) – then a repeater (booster) is neededthen a repeater (booster) is needed

More about LANsMore about LANs The network card fits inside the computer:The network card fits inside the computer:

– either as a separate card either as a separate card – or on the motherboard…or on the motherboard…– uses own softwareuses own software

» works with other software that bind together to control the works with other software that bind together to control the sending and receiving of datasending and receiving of data

If the network is of the client-server type, more If the network is of the client-server type, more complex server software is needed at the complex server software is needed at the “server” end“server” end

If a peer-peer network, connectivity software is If a peer-peer network, connectivity software is less sophisticated…less sophisticated…

More about LANsMore about LANs Other hardware names:Other hardware names:

– Nodes:Nodes: are computers and other intelligent are computers and other intelligent devices with MAC and IP addresses devices with MAC and IP addresses

– Repeaters:Repeaters: boost weak digital signals boost weak digital signals– Hubs:Hubs: link devices & direct data round a link devices & direct data round a

cabling system more efficientlycabling system more efficiently» most hubs are also repeaters most hubs are also repeaters

– SwitchesSwitches: powerful routers that can : powerful routers that can process and filter the data in various ways process and filter the data in various ways way, whilst hubs just send it onway, whilst hubs just send it on

Classification of Networks Classification of Networks by managementby management

Client-Server NetworksClient-Server Networks– networked computers either clients or networked computers either clients or

serversservers Peer-Peer NetworksPeer-Peer Networks

– networked computers all of equal statusnetworked computers all of equal status

Client-Server NetworksClient-Server Networks

A client requests services from a serverA client requests services from a server Client-server interprocess communication Client-server interprocess communication

(IPC) fast and reliable(IPC) fast and reliable Types of clients:Types of clients:

– computer workstation (“fat” client)computer workstation (“fat” client)– computer with limited local storage and computer with limited local storage and

processing (“thin” client)processing (“thin” client)– printer with processing abilityprinter with processing ability

WorkstationsWorkstations Like a standalone computer in many Like a standalone computer in many

respects.respects. Differences:Differences:

– additional hardwareadditional hardware» e.g. network carde.g. network card

– include the basic networking software required:include the basic networking software required:» to allow connection to the networkto allow connection to the network» to communicate effectively with other network nodesto communicate effectively with other network nodes

All computers in a peer-peer network are All computers in a peer-peer network are workstationsworkstations

ServersServers High-powered computersHigh-powered computers

– high storage capacityhigh storage capacity– a lot of memorya lot of memory

Provides network services which are access Provides network services which are access by users through clientsby users through clients– requires a highly specialized software called a requires a highly specialized software called a

Network Operating System (NOS)Network Operating System (NOS)

Examples Network Operating Systems:Examples Network Operating Systems:– Windows NT/2000/XP/2003/VistaWindows NT/2000/XP/2003/Vista– NetwareNetware– UNIX e.g. LinuxUNIX e.g. Linux

Servers in small networksServers in small networks

Scenario: a single Scenario: a single serverserver is the central is the central controlling pointcontrolling point

The The server server also looks after also looks after securitysecurity on the on the network:network:– only allows valid users to log ononly allows valid users to log on– only allows access to resources for users that only allows access to resources for users that

have logged onhave logged on– stores appropriate “user rights” for access to its stores appropriate “user rights” for access to its

files and directoriesfiles and directories

Servers in small networksServers in small networks This same server offers all the normal This same server offers all the normal

network services:network services:– ApplicationsApplications

» when a user wants to use an application on the when a user wants to use an application on the server, it accesses the software server, it accesses the software fromfrom the the serverserver

– PrintingPrinting» the user selects a printer via the serverthe user selects a printer via the server

– File AccessFile Access» users with permission directly access files on users with permission directly access files on

the serverthe server

Problems with this Scenario?Problems with this Scenario?

Discussion in Groups…Discussion in Groups…

Possible Solutions?Possible Solutions?

Further Discussion…Further Discussion…

Servers in Larger NetworksServers in Larger Networks

Larger networks have MANY servers (the Larger networks have MANY servers (the University ITS network currently has at University ITS network currently has at least 50)least 50)

functions can be distributed around functions can be distributed around different individual servers. Examples:different individual servers. Examples:– Login ServerLogin Server– File and Print serverFile and Print server– Applications ServerApplications Server– Internet GatewayInternet Gateway

Login Servers Login Servers (the most crucial!)(the most crucial!)

Dedicated to logging on usersDedicated to logging on users– database of usernames/passwordsdatabase of usernames/passwords

Only allows a potential user to access the Only allows a potential user to access the network if both username and password network if both username and password exactly correspond with entries in the exactly correspond with entries in the databasedatabase– In Windows networks known as In Windows networks known as Domain Domain

ControllersControllers

Peer-Peer networksPeer-Peer networks

Also known as Also known as workgroupsworkgroups No central serverNo central server Computer nodes can act as both clients Computer nodes can act as both clients

and serversand servers No expensive powerful machine No expensive powerful machine

dedicated to providing servicesdedicated to providing services

Peer-Peer networksPeer-Peer networks

No servers!No servers! All users have the following responsibilities:All users have the following responsibilities:

– security & network administrationsecurity & network administration– provide access to their computer’s services provide access to their computer’s services

and resourcesand resources

Advantages & disadvantages Advantages & disadvantages of Client-Server, compared to of Client-Server, compared to

Peer-peerPeer-peer

In groups…In groups… Don’t look at next slides!Don’t look at next slides!

Advantages of a client-server Advantages of a client-server network, compared to a network, compared to a

workgroupworkgroup

Centralised securityCentralised security Centralised access to resourcesCentralised access to resources Centralised network administrationCentralised network administration With more than about 10 users, much With more than about 10 users, much

easier to manage than a workgroup. easier to manage than a workgroup. Can handle up to thousands of usersCan handle up to thousands of users

Disadvantages of client-Disadvantages of client-server, compared to a server, compared to a

workgroupworkgroup Expensive dedicated computer not Expensive dedicated computer not

accessible to usersaccessible to users Expensive server operating system Expensive server operating system

neededneeded Network management requiredNetwork management required Reduces user autonomyReduces user autonomy If the server goes down, the network If the server goes down, the network

ceases to functionceases to function

Thanks for listening Thanks for listening